Display unit

Abstract

A display unit including an indicator (1) for projecting a predetermined image, an image forming optical system (3) for forming a real image at a predetermined position according to the image projected by the indicator, and a transparent hologram screen (10) disposed at the image forming position of the image forming optical system to diffract the real image in a predetermined direction with a directivity.

We claim: 
     
       1. A display unit comprising an indicator (1) for projecting a predetermined image, an image forming optical system (3) for forming a real image at a predetermined position according to the image projected by the indicator, and a transparent hologram screen (10) disposed at the image forming position of the image forming optical system to diffract the real image in a predetermined direction with a directivity. 
     
     
       2. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a reflection-type hologram (4) having a function of converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into a spherical wave light which convergently propagates toward the eyes of an observer located in a space on the same side of the hologram as that of the image forming optical system. 
     
     
       3. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a reflection-type hologram (4) composed of multilayered holograms for diffracting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system toward a plurality of spots around the eyes of an observer located in a space on the same side of the hologram as that of the image forming optical system. 
     
     
       4. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a reflection-type hologram (4) composed of a plurality of holograms which are multi-recorded on a single photosensitive medium to diffract, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system toward a plurality of spots around the eyes of an observer located in a space on the same side of the hologram as that of the image forming optical system. 
     
     
       5. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a reflection-type hologram (4) composed of a first hologram (4a) and a second hologram (4b) which are multilayered, the first hologram converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a first spot located in a space on the same side of the hologram as that of the image forming optical system, the second hologram (4b) converting, with respect to a wavelength among spectra of the indicator light, spherical wave light which divergently propagates from the pupil position of the image forming optical system, into spherical wave light which convergently propagates toward a second spot located in a space on the same side of the hologram as that of the image forming optical system, the two different first and second spots being selected by the left eye and the right eye (6a, 6b) of an observer. 
     
     
       6. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a reflection-type hologram (4) composed of a first hologram (4a) and a second hologram (4b) which are multi-recorded on a single photosensitive medium layer, the first hologram converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a first spot located in a space on the same side of the hologram as the image forming optical system exists, the second hologram (4b) converting, with respect to a wavelength among spectra of the indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a second post located in a space on the same side of the hologram as that of the image forming optical system, the two different first and second spots being selected by the left aye and the right eye (6a, 6b) of an observer. 
     
     
       7. A display unit as set forth in claim 2, wherein a wavelength band-pass filter (8) for selectively transmitting light whose wavelength is in a selected reflective wavelength width of the reflection-type hologram is disposed in an optical path between the reflection-type hologram (4) and the indicator (1). 
     
     
       8. A display unit as set forth in claim 2, wherein an optical path folding mirror (8) having wavelength selectivity for selectively reflecting light whose wavelength is in a selected reflective wavelength width of the reflection-type hologram, is disposed in an optical path between the reflection-type hologram (4) and the indicator (1). 
     
     
       9. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a transmission-type hologram (4') having a function of converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into a spherical wave light which convergently propagates toward an eye of an observer located in a space on the opposite side of the hologram with respect to the image forming optical system. 
     
     
       10. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a transmission-type hologram (4') composed of multilayered holograms for diffracting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, toward a plurality of spots around the eyes of an observer located in a space on the opposite side of the hologram with respect to the image forming optical system. 
     
     
       11. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a transmission-type hologram (4') composed of a plurality of holograms which are multi-recorded on a single photosensitive medium to diffract, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, toward a plurality of spots around the eyes of an observer located in a space on the opposite side of the hologram with respect to the image forming optical system. 
     
     
       12. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a transmission-type hologram (4') composed of a first hologram (4a) and a second hologram (4b) which are multilayered, the first hologram converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a first spot located in a space on the opposite side of the hologram with respect to the image forming optical system, the second hologram (4b) converting, with respect to a wavelength among spectra of the indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a second spot located in a space on the opposite side of the hologram with respect to the image forming optical system, the two different first and second spots being selected by the left eye and the right eye (6a, 6b) of an observer. 
     
     
       13. A display unit as set forth in claim 1, wherein the transparent hologram screen (10) comprises a transmission-type hologram (4b') composed of a first hologram (4a) and a second hologram (4b) which are multi-recorded on a single photosensitive medium layer, the first hologram converting, with respect to a wavelength among spectra of indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a first spot located in a space on the opposite side of the hologram with respect to the image forming optical system, the second hologram (4b) converting, with respect to a wavelength among spectra of the indicator light, spherical wave light which divergently propagates from the position of the image forming optical system, into spherical wave light which convergently propagates toward a second spot located in a space on the opposite side of the hologram with respect to the image forming optical system, the two different first and second spots being selected by the left eye and the right eye (6a, 6b) of an observer. 
     
     
       14. A display unit as set forth in claim 1, wherein the image forming optical system is provided with a variable aperture diaphragm (9) for controlling a visible range of a displayed image. 
     
     
       15. A display unit as set forth in claim 1, wherein the transparent hologram screen comprises a transparent curved substrate (10') having a hologram, and the image forming optical system has field curvature aberration for forming an image on the curved hologram screen according to a planar image provided by the indicator. 
     
     
       16. A display unit as set forth in claim 1, wherein the hologram screen comprises a reflection-type hologram (13), which deflects the real image toward the positions of eyes (6a, 6b) of a user due to a light diffracting phenomenon of the hologram so that the user can see the image on the reflection-type hologram (13), the reflection-type hologram (13) reflecting light having a wavelength band around a wavelength λ1 toward the position of one (6a) of the eyes of the user while reflecting light having a wavelength band around a wavelength λ2 which is different from the wavelength λ1 toward the other eye (6b) of the user, so that the user can see the image with the light of different wavelength bands through the left eye and the right eye.   
     
     
       17. A display unit as set forth in claim 16, wherein the reflection-type hologram (13) comprises a first reflection-type hologram (13a) for reflecting the light having a wavelength band around the wavelength λ1 and a second reflection-type hologram (13b) for reflecting the light having a wavelength band around the wavelength λ2, the holograms being adhered to each other to form a two-layer structure. 
     
     
       18. A display unit as set forth in claim 16, wherein the reflection-type hologram (13) comprises a first reflection-type hologram (13a) for reflecting the light having a wavelength band around the wavelength λ1 and a second reflection-type hologram (13b) for reflecting the light having a wavelength band around the wavelength λ2, the holograms being multi-recorded on a single hologram medium. 
     
     
       19. A display unit as set forth in claim 16, wherein a difference between the wavelengths λ1 and λ2 is selected to be substantially equal to a reflective wavelength band width of the first and second reflection-type holograms (13a, 13b) so that reflective spectra of the first and second reflection-type holograms (13a, 13b) may overlap a little to reduce the difference between the wavelengths λ1 and λ2. 
     
     
       20. A display unit as set forth in claim 16, wherein the wavelengths λ1 and λ2 are selected such that the indicator means can produce an image to be reflected by the first reflection-type hologram (13a) but not by the second reflection-type hologram (13b), as well as an image to be reflected by the second reflection-type hologram (13b) but not by the first reflection-type hologram (13a). 
     
     
       21. A display unit as set forth in claim 20, wherein an indicator (1) produces an image for the left eye and an image for the right eye with the light having wavelength bands around the wavelengths λ1 and λ2, respectively, according to a parallax of the left eye (6a) and right eye (6b), so that the user can obtain a stereoscopic vision. 
     
     
       22. A display unit as set forth in claim 1, wherein the hologram screen comprises a reflection-type hologram (13), which deflects the real image toward the positions of eyes (6a, 6b) of a user due to a light diffracting phenomenon of the hologram so that the user can see the image on the reflection-type hologram (13), the reflection-type hologram (13) reflecting light having N wavelength bands around N different wavelengths λ1, . . . λ2 (N>2) toward the positions of the left eye and the right eye of the user of the display unit or toward a plurality of positions around the eyes of the user, so that the user of the display unit can see the image with a mixture of colors of the plurality of wavelength bands.   
     
     
       23. A display unit as set forth in claim 22, wherein the reflection-type hologram (13) is made by multi-recording a plurality of interference fringes on a single hologram medium. 
     
     
       24. A display unit as set forth in claim 22, wherein the reflection-type hologram (13) is made by laminating a plurality of hologram films. 
     
     
       25. A display unit as set forth in claim 22, wherein the N different wavelengths λ1, . . . λn are selected to have substantially the same intervals as in the reflective wavelength bands of the reflection-type hologram (13). 
     
     
       26. A display unit as set forth in claim 1, wherein the hologram screen (61) comprises reflection-type or transmission-type holographic lenses (63) arrayed on a single medium layer (73), the incident axes and outgoing axes of the holographic lenses being oriented differently from one another, little by little. 
     
     
       27. A display unit as set forth in claim 26, wherein the incident axes of the holographic lenses (63) of the hologram screen (61) pass through a principal point of the projection lens system (3) while the outgoing axes thereof pass through the positions of eyes (6a, 6b) of a user of the display unit. 
     
     
       28. A display unit as set forth in claim 26, wherein the hologram screen comprises a reflection-type hologram which is formed by arranging lens array plates 75 on each side of a holographic plate and by irradiating the holographic plate (70) with coherent light through the lens array plates. 
     
     
       29. A display unit as set forth in claim 26, wherein the hologram screen comprises a transmission-type hologram.